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Add explicit-endian String::from_utf16 variants #95967

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merged 4 commits into from
Oct 11, 2023
Merged

Add explicit-endian String::from_utf16 variants #95967

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8047f8f
Add feature(str_from_utf16_endian)
CAD97 Apr 12, 2022
3d448bd
style nits
CAD97 Sep 29, 2023
1efea31
add str_from_utf16_endian tracking issue
CAD97 Sep 29, 2023
5facc32
fix char imports
CAD97 Sep 29, 2023
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150 changes: 150 additions & 0 deletions library/alloc/src/string.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -714,6 +714,156 @@ impl String {
.collect()
}

/// Decode a UTF-16LE–encoded vector `v` into a `String`, returning [`Err`]
/// if `v` contains any invalid data.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// #![feature(str_from_utf16_endian)]
/// // 𝄞music
/// let v = &[0x34, 0xD8, 0x1E, 0xDD, 0x6d, 0x00, 0x75, 0x00,
/// 0x73, 0x00, 0x69, 0x00, 0x63, 0x00];
/// assert_eq!(String::from("𝄞music"),
/// String::from_utf16le(v).unwrap());
///
/// // 𝄞mu<invalid>ic
/// let v = &[0x34, 0xD8, 0x1E, 0xDD, 0x6d, 0x00, 0x75, 0x00,
/// 0x00, 0xD8, 0x69, 0x00, 0x63, 0x00];
/// assert!(String::from_utf16le(v).is_err());
/// ```
#[cfg(not(no_global_oom_handling))]
#[unstable(feature = "str_from_utf16_endian", issue = "116258")]
pub fn from_utf16le(v: &[u8]) -> Result<String, FromUtf16Error> {
if v.len() % 2 != 0 {
return Err(FromUtf16Error(()));
}
match (cfg!(target_endian = "little"), unsafe { v.align_to::<u16>() }) {
(true, ([], v, [])) => Self::from_utf16(v),
_ => char::decode_utf16(v.array_chunks::<2>().copied().map(u16::from_le_bytes))
.collect::<Result<_, _>>()
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Maybe it would be better to use String::with_capacity() + String::push() instead of collect::<Result<_, _>>() until #48994 is fixed?

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Doing this would match the implementation in from_utf16. However, I expect these functions will be much less performance critical, so adding the extra code is perhaps unneeded? I'm not sure.

.map_err(|_| FromUtf16Error(())),
}
}

/// Decode a UTF-16LE–encoded slice `v` into a `String`, replacing
/// invalid data with [the replacement character (`U+FFFD`)][U+FFFD].
///
/// Unlike [`from_utf8_lossy`] which returns a [`Cow<'a, str>`],
/// `from_utf16le_lossy` returns a `String` since the UTF-16 to UTF-8
/// conversion requires a memory allocation.
///
/// [`from_utf8_lossy`]: String::from_utf8_lossy
/// [`Cow<'a, str>`]: crate::borrow::Cow "borrow::Cow"
/// [U+FFFD]: core::char::REPLACEMENT_CHARACTER
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// #![feature(str_from_utf16_endian)]
/// // 𝄞mus<invalid>ic<invalid>
/// let v = &[0x34, 0xD8, 0x1E, 0xDD, 0x6d, 0x00, 0x75, 0x00,
/// 0x73, 0x00, 0x1E, 0xDD, 0x69, 0x00, 0x63, 0x00,
/// 0x34, 0xD8];
///
/// assert_eq!(String::from("𝄞mus\u{FFFD}ic\u{FFFD}"),
/// String::from_utf16le_lossy(v));
/// ```
#[cfg(not(no_global_oom_handling))]
#[unstable(feature = "str_from_utf16_endian", issue = "116258")]
pub fn from_utf16le_lossy(v: &[u8]) -> String {
match (cfg!(target_endian = "little"), unsafe { v.align_to::<u16>() }) {
(true, ([], v, [])) => Self::from_utf16_lossy(v),
(true, ([], v, [_remainder])) => Self::from_utf16_lossy(v) + "\u{FFFD}",
_ => {
let mut iter = v.array_chunks::<2>();
let string = char::decode_utf16(iter.by_ref().copied().map(u16::from_le_bytes))
.map(|r| r.unwrap_or(char::REPLACEMENT_CHARACTER))
.collect();
if iter.remainder().is_empty() { string } else { string + "\u{FFFD}" }
}
}
}

/// Decode a UTF-16BE–encoded vector `v` into a `String`, returning [`Err`]
/// if `v` contains any invalid data.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// #![feature(str_from_utf16_endian)]
/// // 𝄞music
/// let v = &[0xD8, 0x34, 0xDD, 0x1E, 0x00, 0x6d, 0x00, 0x75,
/// 0x00, 0x73, 0x00, 0x69, 0x00, 0x63];
/// assert_eq!(String::from("𝄞music"),
/// String::from_utf16be(v).unwrap());
///
/// // 𝄞mu<invalid>ic
/// let v = &[0xD8, 0x34, 0xDD, 0x1E, 0x00, 0x6d, 0x00, 0x75,
/// 0xD8, 0x00, 0x00, 0x69, 0x00, 0x63];
/// assert!(String::from_utf16be(v).is_err());
/// ```
#[cfg(not(no_global_oom_handling))]
#[unstable(feature = "str_from_utf16_endian", issue = "116258")]
pub fn from_utf16be(v: &[u8]) -> Result<String, FromUtf16Error> {
if v.len() % 2 != 0 {
return Err(FromUtf16Error(()));
}
match (cfg!(target_endian = "big"), unsafe { v.align_to::<u16>() }) {
(true, ([], v, [])) => Self::from_utf16(v),
_ => char::decode_utf16(v.array_chunks::<2>().copied().map(u16::from_be_bytes))
.collect::<Result<_, _>>()
.map_err(|_| FromUtf16Error(())),
}
}

/// Decode a UTF-16BE–encoded slice `v` into a `String`, replacing
/// invalid data with [the replacement character (`U+FFFD`)][U+FFFD].
///
/// Unlike [`from_utf8_lossy`] which returns a [`Cow<'a, str>`],
/// `from_utf16le_lossy` returns a `String` since the UTF-16 to UTF-8
/// conversion requires a memory allocation.
///
/// [`from_utf8_lossy`]: String::from_utf8_lossy
/// [`Cow<'a, str>`]: crate::borrow::Cow "borrow::Cow"
/// [U+FFFD]: core::char::REPLACEMENT_CHARACTER
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// #![feature(str_from_utf16_endian)]
/// // 𝄞mus<invalid>ic<invalid>
/// let v = &[0xD8, 0x34, 0xDD, 0x1E, 0x00, 0x6d, 0x00, 0x75,
/// 0x00, 0x73, 0xDD, 0x1E, 0x00, 0x69, 0x00, 0x63,
/// 0xD8, 0x34];
///
/// assert_eq!(String::from("𝄞mus\u{FFFD}ic\u{FFFD}"),
/// String::from_utf16be_lossy(v));
/// ```
#[cfg(not(no_global_oom_handling))]
#[unstable(feature = "str_from_utf16_endian", issue = "116258")]
pub fn from_utf16be_lossy(v: &[u8]) -> String {
match (cfg!(target_endian = "big"), unsafe { v.align_to::<u16>() }) {
(true, ([], v, [])) => Self::from_utf16_lossy(v),
(true, ([], v, [_remainder])) => Self::from_utf16_lossy(v) + "\u{FFFD}",
_ => {
let mut iter = v.array_chunks::<2>();
let string = char::decode_utf16(iter.by_ref().copied().map(u16::from_be_bytes))
.map(|r| r.unwrap_or(char::REPLACEMENT_CHARACTER))
.collect();
if iter.remainder().is_empty() { string } else { string + "\u{FFFD}" }
}
}
}

/// Decomposes a `String` into its raw components.
///
/// Returns the raw pointer to the underlying data, the length of
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